Vented explosion-proof lighting fixture



Nov. 14, 1950 N. A. TORNBLOM 2,530,135

VENTED EXPLOSION-PROOF LIGHTING FIXTURE Filed May 7, 1948 Ina en tor hils 7Zrnblom Patented Nov. 14, 1950 VENTED EXPLOSION-PROOF LIGHTING FIXTURE Nil s A. Tornhlom Chicago, Ill., assignor to Apple:

ton Electric Company, Chicago, 111., a corporation of Illinois Application May- 7-, 1948, Serial No. 25,731

7 Claims. (01. 2411-112) 4 he Presen ventio re at o elec rics i h l s xture in ge er l nd mo e srec fieel t a novel, ex o ionprqoi l hti an .e which find p ula b t y o -mews xcl sive ut lit n Pl fi 1 7! 3.51 f fi fih rch mis e eeis a hes z ie pe ating reams- In h de ign of i h fixt re i. thi i re e nsisie e m1li-.- i n to. v nts- I QE P$$i 2 l i 951 .19 F9? e a ple, an ele t al tree-kiwi; e ns w h the! fixtur q ihe esiu i leadin i riq w ld. res-11.1 m h es a li ment of ar Sime .exrlo a eb istens re imeeal u e?! e ee eiib .Wh r they are surrounded b atmosphere pontainingim flammable and evenexplosivQmixtures oils-ais es, vapors or dust particles, an internal eleetrical failure in an improperly designed fixture could easily lead-to an'explosio'n or a "serious fire. To guard against contingencies of this nature, the potential arcing portions of the fixture are cornpletely housed and segregated from the surrounding atmosphere so as tic-preclude the ignitiori'of inflammable or explosive gases in the latter due to arcing or to the ignition within the fixture of inflammable or explosive gases whichrnight have filtered in from the surrounding atmosphere.

' One of the objects f the invention is to provide an explosionproof lighting fixture of extremely light weight but which can be used-with absolute safety in applications where such fixtures are required.

Another object is to provide afixture of the character'setfor-th and capable of dissipating gas pressure from the interior of the fixture at a rate approaching that at which such pressure builds up thus keeping-the peak pressure. within the fixture at aminirnum;

A further object is to provide an explosionproof lightingfix-ture of the type set forth 'andwhich will be capable of dissipating internal gas pressure without permitting the leakage of any flame from the fixturea I Another object is t provide a fixture of the above type which can be quickl installed and readily adapted for use 'with lamps of various tailed description proceeds, takenin the light of heraceon nanr ne rawing, th rein-;

Figure l is an elevational view of a fixture embodying the invention a portion of the external While the invention is susceptible of various modifications and alternative constructions, "a preferred embodiment has been shown in the drawings and will be described below in considerable detail. It should be understood, however,

\ that there is no'intentio n to limit the invention to the specific form disclosed'but on the eon trary, the intention is to cover all modifications and alternative constructions falling within th e spirit and scope of the inventio j'as expressed in the appen ded claims. I v

m9 s 1i t ierenee 0 1 1 dr win it will be noted that the invention isth exempl fie in e is inbi assu a wh ii i the resent instance is adapted to house an ine candescent lamp ll, The, fixture It is, organized 1 a op I2 w ich ca h m m dro an ap pr ate ov rh ad r Wal Support, (not shown). Detachably secured tothe, canopy I2 as by threaded engagement therewith and arranged in surrounding. relationshipwith the lower portion of the canopy is a bellshaped housing [4. he l tter has a carefully machined upper edge portion 15 arranged to sealingly engage a stop shoulder 16 on the canopy, the housing being lockedin place on the-latter as by means of set screws I3. Mounted in sealing abutment with i an. annular face [9- at theilowerend of the housing I l-and secured inplace by means of a suita bly threaded retainer ring 20 is a globe 21 of" heat resistant glass. The ring-20 may, of course, be locked in position by the use of a set screw 22. The globe 2| of the I illustrative fixture I0 is fashioned in the shape of an inverted dome and, together with the housing l4, defines an enclosed lamp chamber 24. Depending upon the application of the fixture the globe 2! may betr'ans parent, translucent, or colored. To support the lamp ll within the chamber 24, a socket 25is provided. The latter is de'pendably mounted upon the underside of the canopy I 2: in any appropriate manner, as by means of a mounting plate 26 and a series of mountingscrews 2-1.

The canopy I2 is of somewhat conventional shape, comprising a hollow body 28 which contains a terminal chamber 29 arranged to communicate with a power supply conduit via a threaded opening 30. Depending from the upper portion of the body 28 is a unitary cage 3| partially enclosing the lower region of the terminal chamber and of smaller diameter than the upper portion of the body. Housed within the terminal chamber 29 and rigidly fixed to the cage 3| is a terminal block 32 to which the power supply leads can be connected, access to the block 32 being had by way of the openings in the canopy walls defining the cage 3|. The block 32, in turn, is connected to the lamp socket by means of insulated leads 33 which pass through a sealing well 34 in the bottom wall of the cage 3|. The well 34 may be filled with material such I as porcelain cement which will be capable of effecting a gas tight and flame tight seal between the leads 33 and the surrounding bore of the well 34.

Provision is made for isolating the terminal chamber 29 from the lamp chamber 24 as to the passage of flame therebetween yet permitting the venting into the lamp chamber of gas pressure generated within the terminal chamber 29 or the power supply conduit leading thereinto. This is accomplished in the present instance by interposing between the chambers 29 and '24 a partition wall of a porous material having high heat conductivity. Preferably, such material is embodied in a generally cylindrical collar 35 of sintered metal such as bronze. In the illustrative fixture l9, the collar 35 is arranged to take advantage of an annular shoulder 38 defined in the canopy wall as a result of the difference between the diameters of the cage 3| and the upper portion of the canopy. Accordingly, one of the end faces of the collar 35 is enlarged as at 36 to form a relatively wide annular surface adapted to sealingly abut against the shoulder 38 when the collar is disposed in surrounding relationship with the cage 3|. To maintain the collar 35 in such condition and thus block off the cage openings which would normally communicate with both the chambers 24 and 29, the lower peripheral portion of the cage 3| together with a portion of the bore in the collar 35 are provided with coacting threads 39. The latter are, of course, machined with sufiicient accuracy to constitute a satisfactory gas tight seal between the collar and the cage. Positive means such as one or more set screws 40 may be utilized for preventing the .collar from being unscrewed, the screws being located so as to engage a relieved annular portion 4| immediately below the threads on the cage 3|.

Means is provided for dissipating gas pressure occurring within the lamp chamber 24 into the atmosphere surrounding the fixture without the leakage of flame from the latter and without danger of igniting such atmosphere. This is accomplished in the present instance by perforating the wall of the housing I 4 with one or more relatively small vent holes 42 and by interposing between such holes and the lamp chamber 24 an additional partition wall of porous material having a high heat conductivity. The holes 42 are preferably arranged in circumferentially spaced relation about the upper po tion of the housing, being blocked off by means of a porous metallic co lar 44. The latter is similar in character to the collar 35 but is of sufficiently larger diameter to permit being mounted in surrounding relationship with 36- spect to the collar 35. In the illustrative fixture H], the collar 44 assumes the shape of a hollow cylinder having smoothly finished annular end faces 45 disposed in abutment with corresponding annular sealing faces 48 formed within the lamp chamber 24. Thus it will be appreciated that any gas vented into the surrounding atmosphere from the lamp chamber 24 must first pass through the tortuous frictional path presented by the collar 44, subsequently entering the holes 42 which ofier further friction to the flow of gas.

To make certain that gas pressure generated within the lamp chamber 24 will be vented to the atmosphere outside the fixture rather than into the terminal chamber 29, the collar 44 is formed with a lower frictional resistance to the flow of gas than the collar 35. This is conveniently accomplished in the present instance by making the collar 44 more porous and the collar 35 less porous. By the same token, the decreased porosity of the collar 35 gives it better machining properties than it would ordinarily have, thus insuring a tight seal along the threads 39 which secure the collar 35 to the canopy.

In order to readily adapt the fixture ID for use with lamps of various sizes, the housing I4 is split into an upper skirt 48 and a lower skirt 49 detachably connected thereto. The skirts 48 and 49 may convenientlybe threaded together and retained in such condition as by means of set screws 50. With this arrangement, a given fixture can be quickly conditioned to accommodate various sizes of lamps merely by interposing lower skirts of various lengths between the upper skirt 48 and the glass globe 2|. Such construction also provides a ready expedient for clamping the second or outermost porous metallic collar 44 securely in place.

For the purpose of obtaining a gas tight seal between the globe 2| and the lower skirt 43 without the use of special tools, the marginal edge portion of a shoulder 49A on the lower skirt is formed with a plurality of circumferentially spaced notches 5|, any one of the latter being adapted to serve as a fulcrum point for the end ofa screwdriver 52. By the same token, the ring 20 is equipped with a radially projecting lug 54 underlying the shoulder 49A and the notches 5|. Thus, it is possible to either tighten or loosen the ring 20 by merely inserting the tip of the screwdriver 52 into one of the notches 5| and pushing the screwdriver in a generally horizontal direction so as to accost the lug 54. By the use of this arrangement, suflicient torque can be applied to the ring 20 to obtain a very satisfactory seal be tween the globe 2| and the surface skirt 49. U

In operation, any gas under pressure developed within the supply conduit or the terminal chamber 29 must pass through the porous metallic collar 35 on its way to the lamp chamber 24. Due to the tremendous friction presented by the collar 35 to the flow of gas therethrough, a certain amount of pressure will be immediately dissipated in overcoming such friction. Furthermore, any flame within the chamber 29 will bedenied escape by the collar 35, since any burning gas entering the latter will be immediately cooled well below its ignition temperature due to the rapid heat conduction properties of the material in the collar and also to the large heat transfer area presented by the labyrinths in its structure. Gas under pressure within the chamber 24, on the other hand, must pass through the tortuous path pre- IQ of the lower sented by the collar 44 and the holes 42 before venting to the atmosphere. Here again a certain amount of pressure will be dissipated within the collar 44 in overcoming the internal friction of the latter, while still additional pressure will be dissipated due to frictional loss in the vent holes 42. Should thegas within the lamp chamber-.24 become ignited, the porous metallic collar 44, will rapidly conduct heat away in the. same manner as the collar 35 so, as. to cool the gas below its ignition point and safely preclude the escape of flame from the fixture.

While the friction presented by both of the collars 35. and 44 to the flow of gas therethrough is far from negligible, such friction is sumciently low to permit the dissipationof gas pressurefrom the fixture at a rate approaching that at which such pressure could build up should any gas therein become ignited. Thus the peak pressure due to an explosion or ignition of gas within either chamber of the fixture can be held down to a safe minimum. As a result of the foregoing, it becomes possible to effect very substantial savings in the weight and manufacturing cost of an explosionproof lighting fixture by reducing the thickness of both the glass and the metallic wall members, at the same time simplifying the construction of the joints between these members. Furthermore, such savings are accomplished with absolute safety since fixtures embodying the invention are arranged to quickly dissipate internal pressure rather than to confine such pressure as is commonly done in earlier fixtures.

A further contribution toward economical construction is realized by the use of a substantial number of conventional or standard parts within the fixture I0. Not only does this reduce manufacturing costs, but in addition, tends to keep mounting costs down since installing personnel will to a large extent be handling simple parts with which they already have a large degree of familiarity.

I claim as my invention:

1. An explosionproof lighting fixture having terminal and lamp chambers therein and comprising, in combination, a housing, a first porous metallic wall totally enclosed within said housing and interposed between said terminal and lamp chambers, said first porous metallic wall being adapted to permit the dissipation of gas pressure from the former into the latter, and a second porous metallic wall also totally enclosed within said housing but located so as to block off direct communication between the lamp chamber and the exterior of said housing, said second porous metallic wall being adapted to conduct gas under pressure from the lam chamber into the atmosphere surrounding said fixture while precluding the leakage of flame from said lamp chamber.

2. An explosicnproof lighting fixture having a canopy with a terminal chambe therein, said fixture comprising the combination of an upper skirt and a lower skirt, one Of said skirts having a perforated wall portion, a globe detachably fixed to said lower skirt and defining therewith a lamp chamber, a first porous metallic collar disposed in surrounding relationship with a portion of said canopy and threadedly secured thereto, said first collar being interposed between said terminal and lamp chambers and having a relatively high heat conductivity to permit a flow of gas without fiame from said terminal chamber into said lamp chamber, and a second porous metallic collar interposed between the lamp chamber and the perforated wall portion of said one of said skirts, said second porouscollar alsohaving a relatively high heat conductivity to permit a flow of gas without flame from said lamp chamber into the atmosphere surrounding said fixture via the perforated wall portion of said one skirt.

3. An explosionproof lighting fixture having a canopy with a terminal chambe therein, said fixture comprising the combination of an upper skirt having vent holes in the wall thereof and carried by said canopy, a lower skirt dependably supported by said upper skirt, a globe-detachably fixed to said lower skirt and defining a lamp chamber within said skirts, a first porous metallic collar interposed between. said terminal and said lamp chambers and threadedly secured to said canopy, said first porous collar having a relatively high heat conductivity to permit a flow of gas without flame from said terminal chamber into said lamp chamber, and a second porous metallic collar housed within said upper skirt and secured in place by means of said lower skirt, said second porous collar being interposed between said lamp chamber and the vent holes in said upper skirt and having a relatively high heat conductivity to permit a flow of gas without flame from said lamp chamber into the atmosphere surrounding said fixture via the vent holes in said upper skirt.

4. In an explosionproof lighting fixture having a terminal chamber and a lamp chamber, the combination of a canopy, an upper skirt mounted on said canopy and having vent holes in the wall thereof and an annular sealing surface therein, a lower skirt dependably supported by said upper skirt and having an annular sealing surface along its upper end portion underlying the annular sealing surface of said upper skirt, and a porous metallic collar of hollow cylindrical shape interposed between said upper and lower skirts so as to block off from the lamp chamber the vent holes in said upper skirt, said porous collar having end surfaces adapted to abuttingly engage the annular sealing surfaces in said skirts.

5. In an explosionproof lighting fixture of the character set forth, the combination of a canopy having a stepped terminal chamber therein defining an annular shoulder on the underside thereof, a depending cage portion unitary with said canopy and partially enclosing said terminal chamber, said cage portion having threads thereon and being surrounded by said annular shoulder, and a sintered metallic collar threadedly secured to said cage portion, said collar being adapted to complete the enclosing of the terminal chamber by seating tightly against said annular shoulder.

6. In an explosionproof lighting fixture having a terminal chamber and a lamp chamber, the combination of a first porous partition wall of sintered metallic construction interposed between said chambers and adapted to permit gas to fiow therebetween, a second porous partition wall also of sintered metallic construction interposed between one of said chambers and the exterior of said fixture, said second partition wall having a greater porosity than said first partition wall so as to vent gas from said one of said chambers to the exterior of said fixture rather thanto the other of said chambers.

7. An explosionproof lighting fixture having an enclosure including a terminal chamber adapted to communicate with a lamp chamber, the latter being vented to the surrounding atmosphere via one or more holes in said enclosure, said fixture comprising the combination of a first sintered 7 8 metallic collar disposed in surrounding relation REFERENCES CITED Wlth the termmal chamber and adapted to The following references are of record in the duct a flow of gas therefrom, asecond sintered file of this patent: metallic collar mounted in spaced apart concentric relation to said first collar and interposed 5 UNITED STATES PATENTS between the lamp chamber and the vent holes Number Name Date in said enclosure, said second collar having a 489,150 Keil Jan. 3, 1893 lower frictional resistance to the flow of gas than 2,089,049 Benjamin Aug. 3, 1937 said first collar and being adapted to vent gas 2,131,117 Phillips Sept. 27, 1938 from the lamp chamber to the atmosphere rather 10 2,339,670 Benson Jan. 28, 1944 than to the terminal chamber. FOREIGN PATENTS NILS A. TORNBLOM. Number Country Date 26,978 Holland June 15 1927 365,648 Italy Dec. 9, 1938 640,249 France Mar. 24, 1928 

